Sharif Digital Repository

In this report, sessile drop technique was employed to study the wetting of alumina by pure aluminium. Contact angle of pure aluminium on the surface of polycrystalline alumina substrate was studied in the temperature range of 750-1100 °C. Electron microscopy and EDX analysis were employed to examine the possible reactions at the melt-substrate interface. It was found that at temperatures in excess of 1050 °C molten aluminium can wet alumina. No reaction layer was detected at the Al/Al2O3 interface. © 2007 Elsevier B.V. All rights reserved  

In present work, an attempt has been made to investigate the wear behavior of particle reinforced composites based on one of the proper magnesium alloys. The SiCP/QE22 composites and QE22 unreinforced specimens were produced via the powder metallurgy route. The volume fractions of SiC particles with three different shapes, i.e. sharp, blocky and round, were selected in the range of 10-25 vol.%. The dry sliding tests were conducted on unreinforced matrix and SiCP/QE22 composites using pin-on-disk apparatus, according to ASTM G99-95a standard. The applied loads were selected as 3, 5 and 20 N. The tests were carried out under sliding speeds of 0.5 and 1.2 m/s. In all tests, the sliding... 

The fabrication of TixNi1-x shape memory films using simultaneous magnetron sputtering from two separate, elemental targets was investigated. The films were deposited at room temperature and then annealed at 500 °C to achieve the shape memory effect. The influence of sputtering parameters such as power ratio to the targets (to control the composition) and Ar gas pressure (to control the film structure) were studied. It was found that the Ar gas pressure had a critical influence on the shape memory effect of the films. Characterization of the films was carried out by energy dispersive X-ray spectroscopy in a scanning electron microscope (to measure the film composition and uniformity), in... 

The aim of current research is to investigate the substrate electropolishing effect on corrosion resistance of Ni-Mo thin films. For this purpose, corrosion resistance of coatings deposited on mild steel substrates, that was electropolished or mechanically polished, have been compared in 3.5 wt.% NaCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The structural properties of Ni-Mo thin films were evaluated using X-ray diffraction (XRD) and their morphology, microstructure and chemical composition were also investigated using scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). Temperature and acidity of deposition... 

The unique properties of NiTi alloy, such as its shape memory effect, super-elasticity and biocompatibility, make it ideal material for various applications such as aerospace, micro-electronics and medical device. In order to meet the requirement of increasing applications, great attention has been given to joining of this material to itself and to other materials during past few years. Laser welding has been known as a suitable joining technique for NiTi shape memory alloy. Hence, in this work, a comparative study on laser welding of NiTi wire to itself and to AISI 304 austenitic stainless steel wire has been made. Microstructures, mechanical properties and fracture morphologies of the... 

The present work investigates joining of two MoSi2 parts through Cusil/Zr/Cusil interlayer with Cusil being a commercial eutectic of Cu-Ag alloy. The joining operation was implemented in an inert gas tube furnace by brazing. The brazing temperature ranged from 800 to 930°C while the operation lasted for 60min. Evaluation of joints strength through shear loading identified the maximum strength 60.31MPa for the brazed sample at 830°C. Interfacial microstructure was studied by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD) techniques. Applying the temperature of 830°C was led to a uniform dense joint consisting of various phases with... 

In this work, the effects of the annealing temperature and duration on the joint strength of the steel/aluminum lap joints made by friction stir welding were investigated. The strength of the welded joints was evaluated by shear-tensile test. Formation of intermetallic layer at the joint interface and the fracture locations were studied using scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD). The results indicated that longer time of annealing treatment resulted in higher joint strength at 300 and 350 °C and that the rate of the increase in joint strength with time was about 72% higher at the latter temperature... 

The main challenges of biological implants are suitable strength, adhesion, biocompatibility and corrosion resistance. This paper discusses fabrication, characterization and electrochemical investigation of anodized Ti6Al4V without and with a hydroxyapatite (HA) layer, HA/TiO2 nanoparticles (NPs) and HA/TiO2 nanotubes (HA/anodized). X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS) were used to characterize and compare properties of different samples. Dense HA with uniform distribution and 12.8 ± 2 MPa adhesive strength enhanced to 19.2 ± 4 MPa by the addition of TiO2 nanoparticles and enhanced to 23.1 ± 4 MPa by the... 

A simple platform based on a hairpin oligonucleotide switch and multi-walled carbon nanotubes (MWCNTs) for the ultrasensitive detection of specific DNA sequences has been developed. In this approach, the π-stacking interaction of single-strand DNA-MWCNT was employed to construct an electrochemical DNA biosensor. Changes to the surface conductivity, based on the MWCNT replacement, were monitored by using the electrochemical species [Fe(CN)6]3-/4- as a redox probe. Morphological and voltammetric characterizations of the electrode surface were performed using atomic force microscopy (AFM), energy dispersive spectroscopy (EDS), cyclic voltammetry (CV), differential pulse voltammetry (DPV) and... 

In this paper, the failure of the reformer furnace tube, made of HP-Nb micro alloyed heat resistant steel is investigated. The failure was due to a longitudinal crack developing in the circumferential weld joint close to the outlet end of the tube, where the mean wall temperature had reached the highest value during service. According to the temperature records during the period of 7 years of being in service, the tube had experienced temperatures higher than the tubes designed temperature. This situation besides the occurrence of several sudden shutdowns caused the mechanical properties degradation.Macroscopic and microscopic examinations revealed that the failure had occurred due to the... 

Supportless Ni-Pd-0.1CNT foamy nanocatalyst with specific surface area of 611.3 m2/g was produced by electroless deposition of nickel, palladium and multiwall carbon nanotube (MWCNT) on interim polyurethane substrate. Application of temperature programmed reduction (TPR) and temperature programmed oxidation (TPO) data into Kissinger (Redhead) kinetic model showed lessening of their activation energies due to Pd and CNT addition. Presence of foamy Ni/SiC caused 8% higher steam reforming of methane; while Ni-Pd-0.1CNT presence resulted in 22% higher methane conversion. The catalytic behavior of the samples was described by morphological and compositional studies which were carried out by... 

Polyphosphate reduced graphene oxide on Ni foam (PPO-RGO/NF) is synthesized by varying weight ratios of Na5P3O10 (PO): graphene oxide (GO) with a simple, scalable and low cost method through freeze-drying of the PO-GO/NF followed by thermal treatment of the prepared electrodes. The resulting samples are characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), Brunauer-Emmett-Teller (BET), and raman spectroscopy methods. The results show that the weight ratio of PO:GO, considerably affect the... 

The effects of severe plastic deformation on properties of AA1100 and AA2024 including the ultrasound velocity and the shear strength during multi-axial compression (MAC) are studied. Additionally, optical microscopy, scanning electron microscopy, and X-ray energy-dispersive spectroscopy are utilized. For both AA1100 and AA2024, an opposite trend is reported in the shear strength and the sound velocity versus deformation strain of MAC. At high strain range, AA1100 and AA2024 samples reach a plateau in the strength due to the occurrence of dynamic recovery. On the other hand, the sound velocity is shown to decrease 11% and 15% for AA1100 and AA2024, respectively. Furthermore, the... 

In the bone tissue engineering field (BTE), it is of significant importance to develop bioactive multifunctional scaffolds with enhanced osteoconductivity, osteoinductivity, and antibacterial properties required for lost bone tissue regeneration. In this work, a bioactive glass-ceramic scaffold was manufactured via a novel polymer-derived ceramics (PDC) manufacturing method. To gain antibacterial properties, the silver ions were incorporated in controlled amount along with other precursors in the PDC processing stage. Microstructural and structural properties of the fabricated silicate-phosphate glass-ceramic scaffold were evaluated by scanning electron microscopy (SEM) equipped with energy... 

The effect of temperature, pressure and bonding time on microstructure of temperature gradient transient liquid phase (TGTLP) diffusion bonded Al7075 alloy using liquid gallium interlayer was investigated. The selected bonding method relies on using the minimum amount of liquid gallium on faying surfaces, using a very fast heating rate to reach the joining temperature and imposing a temperature gradient across the bond region. The microstructure of the diffusion bonded joints was evaluated by light optical microscopy, scanning electron microscopy and energy dispersive spectroscopy (EDS). Results show that by increasing the temperature, pressure and time of joining, a more uniform... 

In this study, we attempt to characterize the microstructural evolution during friction stir butt welding of Al-Cu-laminated composites and its effect on the fracture behavior of the joint. Emphasis is on the material flow and particle distribution in the stir zone. For this purpose, optical microscopy and scanning electron microscopy (SEM) images, energy-dispersive spectroscopy EDS and XRD analyses, hardness measurements, and tensile tests are carried out on the joints. It is shown that intermetallic compounds exist in lamellas of banding structure formed in the advancing side of the welds. In samples welded from the Cu side, the banding structure in the advancing side and the hook... 

Despite the promise of hydrogel-based stem cell therapies in orthopedics, a significant need still exists for the development of injectable microenvironments capable of utilizing the regenerative potential of donor cells. Indeed, the quest for biomaterials that can direct stem cells into bone without the need of external factors has been the "Holy Grail" in orthopedic stem cell therapy for decades. To address this challenge, we have utilized a combinatorial approach to screen over 63 nanoengineered hydrogels made from alginate, hyaluronic acid, and two-dimensional nanoclays. Out of these combinations, we have identified a biomaterial that can promote osteogenesis in the absence of... 

Nowadays, achievement to easy, fast, reliable and cost-effective techniques and tools is one of the most important challenges in detection of microorganisms. Salmonella typhimurium is one of the most important pathogenic bacteria that affect the human health and environmental infections. In this work we report a new, stable, biocompatible and cost-effective platform for construction of an aptasensor based on nanoporous gold (NPG) for detection of S. typhimurium. Nanoporous gold is electrochemically synthesized using Au-Cu alloy at the surface of Au/GCE. Thiol functionalized aptamer is used for effective linking to the surface of NPG/Au/GCE via self-assemble monolayers (SAMs) formation.... 

Nanostructured W-20 wt% Cu composite powder was synthesized by mechanical alloying (MA) in an Attritor ball mill. The morphological changes and structural evolution of the composite powder during MA was studied by employing scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX), laser particle size analyzer (LPS), inductively coupled plasma (ICP) spectrometry, atomic absorption spectrophotometery (AAS), and the bulk powder density measurement. The results were compared with those obtained from attrition milling of monolithic W and Cu powders processed at the same condition. Whereas the milling mechanism of the monolithic powders follow the ductile (for Cu)... 

Fabrication of high quality zinc oxide thin films and analysis on its physical, chemical properties have applications in opto-electronic devices, UV laser, microelectronics and micro-machining schemes. Highly textured ZnO thin film with a preferred (0 0 2) orientation was prepared by two-stage chemical deposition (TSCD) using an aqueous solution containing zinc complex on a soda-lime glass substrate. From the results obtained, it can be shown that the preferred orientations of the film microcrystal changes with the doping process. The film was characterized by X-ray diffraction (XRD), SEM, EDAX, optical technique, Fourier transform infrared spectroscopy (FTIR) in order to qualify its...